The present invention relates to a scroll fluid machine and especially to a scroll fluid machine in which a stationary wrap of a stationary scroll engages with an orbiting wrap of an orbiting scroll which is eccentrically revolved by an eccentric shaft so that a gas absorbed through the outer circumference is compressed toward the center.
A scroll fluid machine includes a scroll compressor, a scroll vacuum pump, a scroll expander and a scroll blower.
FIG. 3 shows a scroll decompressor for decompressing a separate chamber connected therewith, as one example of a scroll fluid machine, and the left and right sides are deemed to be the front and rear.
A stationary scroll 1 at the front or left side in FIG. 3 comprises a stationary end plate 4 which has an inlet 2 in the outer circumference and an outlet 3 at the center. The stationary end plate 8 has a spiral stationary wrap 5 on the front surface and a plurality of horizontal corrugated cooling fins 6 provided at regular intervals on the rear surface.
An orbiting scroll 7 behind the stationary scroll 1 comprises a circular orbiting end plate 8 which has a spiral orbiting wrap 9 on the front surface opposite to the stationary scroll 1 and a plurality of corrugated cooling fins 10 provided horizontally at regular intervals on the rear surface.
A bearing plate 11 is provided on the rear surface of the orbiting scroll 7. On the center of the rear surface of the bearing plate 11, there is a tubular boss 15 which rotatably supports an eccentric axial portion 13 of a drive shaft 12 via a roller bearing 14 and an oil seal 15a. At three points of the outer circumference of the bearing plate 11, there are known crank-pin-shaped self-rotation preventing mechanisms 16 so that the orbiting scroll 7 may eccentrically be revolved around the drive shaft 12 in a housing 17.
The rear end of the drive shaft 12 projects from the housing 17 and a power-transmitting pulley 18 and a cooling fan 19 are mounted to the rear end. The cooling fan 19 is covered with a cover 20 mounted to the rear surface of the housing 17.
A cover plate 21 is fixed on the front surface of the stationary scroll 1 by a screw 22. The orbiting scroll 7 and the bearing plate 11 are fixed by a screw 23. The rear plate 24 of the stationary scroll 1 is fixed on the housing 17 by a bolt 25 and a nut 26.
Engagement grooves 5a,9a are formed on the stationary wrap 5 and the orbiting wrap 9 respectively. Seal members “S” are put in the engagement grooves 5a,9a and are in sliding contact with the orbiting end plate 8 of the orbiting scroll 7 and the stationary end plate 4 of the stationary scroll 1.
The orbiting scroll 7 is eccentrically revolved with the eccentric axial portion 13 of the drive shaft 12 and the self-rotation preventing mechanisms 16 so that the volume of a spiral sealed chamber between the stationary wrap 5 and the orbiting wrap 9 may reduce gradually toward the center thereby introducing fluid absorbed through the outer circumference to the center to discharge it through the outlet 3.
In the scroll fluid machine, the orbiting scroll 7 is subjected to thrust during operation owing to pressure difference between the front and rear surfaces. Thrust is directed in a certain or forward direction.
As shown in FIG. 4, there is a scroll fluid machine in which two stationary scrolls 1,1 are provided opposite to each other and an orbiting scroll 7 having orbiting wrap 9,9 on the front and rear surfaces respectively. The scroll fluid machine is subjected to such thrust as well. It is inevitable owing to pressure difference which often occurs in front of and behind of the orbiting scroll 7 during operation.
Such thrust acts to the orbiting scroll, so that excessive force acts to the seal members “S” at the ends of the stationary and orbiting wraps. Thus, rotation resistance of the orbiting scroll 7 increases and the seal members “S” are worn and deformed, so that the end of the orbiting wrap 9 directly contacts the stationary end plate 4 to make its original function lost.
To solve the disadvantages, JP 9-329093A, JP 2002-188584A and JP 2003-21084A disclose that the same pole magnets are disposed on opposite surfaces of stationary and orbiting scrolls to keep the orbiting scroll in position by its repulsive force.
JP 9-329093A discloses an annular magnet or a plurality of small magnets arranged annularly on the rear surface of an orbiting scroll which is opposite to a thrust bearing thereby preventing a gap in a sliding surface between the orbiting scroll and the thrust bearing. However, it is not intended to prevent axial motion of the orbiting scroll and such advantage is not achieved.
JP 2002-188584A discloses magnets which are provided in a stationary member and an orbiting scroll respectively to constitute a self-rotation preventing mechanism for preventing self-rotation of the orbiting scroll by magnetic force which acts between the magnet of the stationary member and the magnet of the orbiting scroll. However axial motion of the orbiting scroll is not prevented.
JP 2003-21084A discloses a permanent magnet as supplemental energizing means for generating axial force for pressing an orbiting scroll axially toward a stationary scroll thereby reducing thrust which acts to a sliding contact surface which supports an orbiting scroll axially by a middle housing. However, it is not intended to decrease mutual pressing force between the stationary and orbiting scrolls.